The use and mechanism of reversible control agents for free radical polymerization is now generally known and coined as RAFT (Reversible Addition Fragmentation Transfer), see for example, U.S. Pat. No. 6,153,705, WO 98/01478, WO 99/35177, WO 99/31144, and WO 98/58974, each of which is incorporated herein by reference. Recently new agents have been disclosed which are readily available for polymerizing desired monomers under commercially acceptable conditions, which include high conversion at the shortest possible reaction times and lower temperatures, see for example U.S. Pat. Nos. 6,380,335, 6,395,850, and 6,518,364, each of which is incorporated herein by reference. Olefin Addition-fragmentation agents are also known as conventional chain transfer agents. Some of notable examples are allylic sulfide and ethyleneoxy derivatives. These compounds act as conventional chain transfer agents and allow control over molecular weight and bring functional groups to the polymer termini. However, because the transfer reaction is very slow when compared with dithiocompounds used in RAFT polylmerizations, these addition-fragmentation agents do not provide material with the attributes of living polymerization, i.e. low molecular weight distribution and block architectures. There are currently some limitations to polymers produced by the RAFT process using dithiocarbonylated or dithiophosphorylated control agents. For instance, the polymers may contain one or more functional groups, such as dithioester, dithiocarbonate, dithiocarbazate, or dithiocarbamate, which are normally yellow in color. The appearance potentially limits the polymer's potential applications to such areas as electronics, which may require a clear color. In some cases the dithiocompound might be unstable under the conditions of use, or might degrade upon aging, and generate some unwanted effects such as odor, discoloration, etc.
WO 02/090397 discusses a method of radical reduction of dithiocarbonyl or dithiophosphoryl groups using a free radical intitiator and a compound bearing a labile hydrogen atom. The method disclosed essentially removes the unwanted group from the polymer chain end and replaces it with a hydrogen atom. It does not disclose or teach any other methods for removing unwanted groups from the end of a polymer chain, or replacing those moieties with anything other than hydrogen. The use of a hydrogen labile compound may be undesirable in some circumstances, such as when those compounds are mercaptans, notoriously odoriferous, or alcohols which may be non-solvents of the polymers.
Thus, what is needed is a method for removing certain groups from a chain end of a polymer and replacing them with other groups. The invention accomplishes this without the need for a compound having a labile hydrogen atom.
This invention provides a method for removing unwanted groups from a chain end of a polymer and replacing them with a more desirable group. The invention accomplishes this without the need for a compound having a labile hydrogen atom.
This invention provides control agents that can be easily modified for particular monomers and monomer mixtures. Some of the control agents described herein contain at least one nitrogen-nitrogen bond which allows for simpler modification of the electronic and steric nature of the control agents as compared to known control agents. These modified properties allow for improved conditions of the polymerization process and/or improved properties of the polymers obtained from the processes. This invention also provides a method for removing unwanted groups from a chain end of a polymer and replacing them with a more desirable group. The invention accomplishes this without the need for a compound having a labile hydrogen atom.